Although Drupal is a very powerful tool, its very power causes a few disadvantages:
A short learning curve is needed to get started and use the system effectively.
It is more hardware-intensive than basic static pages. As it's more hardware-intensive and can create performance issues on a server, you may need to make sure that your organization or business can handle the expense of upgrading a server and the overall server infrastructure to support the site. This may include more expensive hosting options
Additional programming may be needed to customize Drupal modules to do exactly what you want. Alternatively, you may have to compromise on desired functionality, based on what is actually available
Drupal may be more vulnerable to security issues as there are a large number of sites that use Drupal, and hackers may target Drupal sites as it's a popular open source software used by many site developers
Along the same lines as security, Drupal sites require frequent module and software updates in order to keep the website secure and stable. This is extremely important in order to keep your Drupal codebase secure
There may be limitations to the framework, which could make building custom functionality more difficult